Zygarde @ Leftovers  
Ability: Power Construct  
EVs: 252 HP / 4 Atk / 252 Def  
Impish Nature  
- Thousand Arrows  
- Rest  
- Dragon Tail  
- Glare  
Physically Defensive Zygarde is a monster. Being able to wall non-HP Ice Marshadow is amazing, among other threats. Thousand Arrows hits nearly everything for neutral damage, Rest is decent recovery due to Zygarde's phenomenal bulk allowing it to sleep for two turns, Dragon Tail forces out Pokemon that try to set up, and Glare cripples offensive switch ins, such as Marshadow and Dusk Mane/Ultra Necrozma.

Marshadow @ Focus Sash  
Ability: Technician  
EVs: 252 Atk / 4 SpD / 252 Spe  
Jolly Nature  
- Spectral Thief  
- Close Combat  
- Swagger  
- Shadow Sneak  

Marshadow @ Focus Sash  
Ability: Technician  
EVs: 252 Atk / 4 SpA / 252 Spe  
Naive Nature  
- Spectral Thief  
- Close Combat  
- Hidden Power [Ice]  
- Shadow Sneak  
I'll combine these two as they do pretty similar things. They are both cleaners/revenge killers, with the former having Swagger to boost its own attack with Spectral Thief while also having the potential to hurt the opponent for one turn while the other Marshadow has HP Ice to hit opposing Zygarde for super effective damage. Double Sash Marshadow is REALLY difficult to deal with in this meta thanks to its ability to easily overwhelm its checks.

Venusaur-Mega @ Venusaurite  
Ability: Thick Fat  
EVs: 252 HP / 4 Def / 252 SpD  
Calm Nature  
IVs: 0 Atk  
- Charm  
- Synthesis  
- Grass Knot  
- Sludge Bomb  
This is legit my favorite Pokemon on this team. Thanks to Charm, Mega Venusaur completely shuts down all variants of Marshadow, even Soul-Stealing Seven Star Strike thanks to Synthesis recovery. Grass Knot Helps vs Zygarde, as it is one of the few moves Venusaur has to break its Substitute, while Sludge Bomb deals decent damage to most things that resist/take little damage from Grass Knot, though I suppose this could be replaced with Leech Seed but idk.

Necrozma-Dusk-Mane @ Ultranecrozium Z  
Ability: Prism Armor  
EVs: 252 Atk / 4 Def / 252 Spe  
Jolly Nature  
- Swords Dance  
- Photon Geyser  
- Sunsteel Strike  
- Earthquake  
Oh boy. This boy is an absolute powerhouse. Dusk Mane's high natural bulk plus Prism Armor let Necrozma more easily set up Swords Dance while being able to feign a Searing Sunraze Smash set. When it transforms into Ultra Necrozma, its power goes through the roof. Photon Geyser hurts like hell and, thanks to Ultranecrozium Z, it becomes Light That Burns the Sky, capable of obliterating even resists. Sunsteel Strike allows it to hurt nearly everything that resist the former. Earthquake in the last slot hurts Steel-types that resist the previous two moves. 

Tapu Lele @ Choice Scarf  
Ability: Psychic Surge  
EVs: 252 SpA / 4 SpD / 252 Spe  
Modest Nature  
IVs: 0 Atk  
- Psychic  
- Moonblast  
- Hidden Power [Fire]  
- Shadow Ball  
This slot I'm honestly not certain of. I've been suggested to use this but It's just felt underwhelming to me. Ngl, I'm looking for replacements for this slot, so any suggestions would be helpful.
Weaknesses:
Marshadow: Having 4/6 of my team weak to this bugger is pretty annoying, though Zygarde and Mega Venusaur help alleviate this pressure quite a lot.
Hazards: Breaking Marshadow's Focus Sash really inhibits its ability to revenge kill, especially against threats like Ultra Necrozma.
Double Necrozma: This combo is difficult to deal with, as Dusk Mane + Ultra Necrozma can easily overwhelm my team when trying to deal with it.